Long term evolution (LTE) systems, i.e., 3.9 generation mobile telephone systems, employ orthogonal frequency division multiplexing (OFDM), which has a frequency repetition number of one in the downlink. Thus, out of concern that increased inter-cell interference at cell boundaries leads to deterioration of throughput, the application of inter-cell interference coordination (ICIC) using a technique of fractional frequency reuse (FFR) is being investigated (see, e.g., Simonsson, A., et al., “Frequency Reuse and Intercell Interference Co-ordination in E-UTRA”, VTC2007-Spring., pp. 3091-3095, 2007 and Wu, Jianming, et al., “Step-Function based Adaptive Fractional Frequency Reuse,” IEICE Tech. Rep., Vol. 108, No. 391, RCS2008-178, pp. 35-38, 2009).
In ICIC of LTE, base stations exchange relative narrowband transmission power (RNTP), which is a signal indicative of the level of transmission power for each band. It is thought that the effects of interference reduction may be improved by using RNTP as compared to FFR, which is static.
In a real environment, it is conceivable that more complicated cell shapes may be formed due to various base station arrangements and radio wave propagation environments and that the distribution of user equipment (UE), i.e., user terminals, varies according to the time of day. Therefore, the development of an algorithm utilizing RNTP such that the effect of ICIC is obtained constantly is demanded to enable adaptation to changes in a complicated environment.
In a conventional FFR mode in which information is not exchanged between cells, a system band is divided into multiple bands and a portion thereof is determined as a cell edge band. The cell edge band is set as a cell-specific parameter for each cell so as to be different from nearby cells as much as possible (see, e.g., “OFDMA Downlink inter-cell interference mitigation”, 3GPP TSG RAN WG1 MEETING #44 R1-060291, Denver, Colo., Feb. 13-17, 2006).
A scheduler in a base station classifies each UE in a cell as a cell edge terminal or a cell center terminal based on the average signal to interference and noise ratio (SINR) of the UE, etc., and schedules the cell edge terminals in the cell edge band. The interference at the cell edge terminals is mitigated by performing transmission using relatively greater electric power for the cell edge terminals and using relatively smaller electric power for the cell center terminals.
However, the conventional techniques have a problem in that it is difficult to appropriately determine a cell edge band for allocating a cell edge terminal in a real environment and interference at the cell edge terminal cannot be mitigated in an efficient manner. In a cell arrangement having a complicated cell shape, it is more difficult to determine the cell edge band. Such a problem is not limited to an LTE system and may occur in other communication systems that perform radio communication.